Method for Fuel Vapor Canister Purging

ABSTRACT

A method of controlling fuel vapor purging in a hybrid electric vehicle capable of selectively operating an internal combustion engine is provided. The method includes, determining a fuel tank condition parameter based on an amount of liquid fuel residing in a fuel tank of the hybrid electric vehicle and a duration since the previous fuel tank filling event, in response to the fuel tank condition parameter exceeding a threshold limit, initiating operation of the internal combustion engine and purging fuel vapor from the fuel vapor canister for a predetermined duration, and in response to the fuel tank condition parameter being less than the threshold limit, selectively purging fuel vapor from the fuel vapor canister based on an engine operating condition.

FIELD OF THE INVENTION

The present application relates to a method for fuel vapor purging,specifically the application relates to a method for fuel vapor purgingin a hybrid electric vehicle.

BACKGROUND AND SUMMARY

During vehicle operation, fuel vapor may be generated in the fuel systemof a vehicle due to heat generated from engine operation, for example.As the amount of fuel vapor increases pressure in the fuel system mayincrease. In order to regulate the fuel system pressure, fuel vapor maybe released from the fuel system. However, releasing fuel vapor to theatmosphere causes an increase in fuel vapor emissions. Accordingly, thefuel system may include a fuel vapor canister to filter fuel vapor uponrelease from the fuel system to prevent the release of fuel vaporemissions. Eventually, the fuel vapor canister may become filled with anamount of fuel vapor. The fuel canister may be cleared of fuel vapor byway of a purging operation. A fuel vapor purging operation may includeopening a purge valve located in the manifold of the internal combustionengine to introduce the fuel vapor into the cylinder(s) of the internalcombustion engine for combustion so that fuel economy may be maintainedand fuel vapor emissions may be reduced. Thus, during a fuel vapor purgeoperation the internal combustion engine is required to be operating inorder to provide engine vacuum to draw the fuel vapor from the fuelvapor canister into the cylinder(s) as well as to provide combustion forthe fuel vapor.

In a hybrid electric vehicle, in order to achieve gains in fuel economyand powertrain efficiency the internal combustion engine may not alwaysbe operating. Accordingly, the opportunity for fuel vapor purging may belimited even though fuel vapor may still be accumulating in the fuelvapor canister.

One approach to control fuel vapor purge involves purging based on thefuel tank pressure and the amount of time since the last purgeoperation. Based on one or more of those indicators exceeding athreshold, the internal combustion engine may be turned on so that thefuel vapor canister may be purged. See, for example, U.S. Pat. No.6,557,534.

However, the inventors herein have recognized that the above approachhas some issues. In particular, under some conditions, the internalcombustion engine may be started unnecessarily in order to perform thefuel vapor purge operation. For example, since the above approach onlypurges when the fuel vapor canister is substantially full hybridelectric operation may be interrupted unnecessarily in order to performa purging operation. By turning on the internal combustion engine solelyto perform a purge operation the operating efficiency of the hybridelectric vehicle may be reduced since additional fuel may be consumed tostart the engine, for example. Furthermore, an increase in engine startevents may reduce operating transparency to the vehicle operator.

The above issues may be addressed by, in one example, a method ofcontrolling fuel vapor purging in a hybrid electric vehicle capable ofselectively operating an internal combustion engine, the methodcomprising: determining a fuel tank condition parameter based on anamount of liquid fuel residing in a fuel tank of the hybrid electricvehicle and a duration since a previous fuel tank filling event; inresponse to the fuel tank condition parameter exceeding a thresholdlimit, initiating operation of the internal combustion engine andpurging fuel vapor from the fuel vapor canister for a predeterminedduration; and in response to the fuel tank condition parameter beingless than the threshold limit, selectively purging fuel vapor from thefuel vapor canister based on an engine operating condition.

Thus, by performing fuel vapor purging based on the condition of thefuel tank, the state of the fuel vapor canister may be regulated toprevent fuel vapor emissions from being released to the atmosphere andoperating the internal combustion engine only for fuel vapor purgingpurposes may be reduced which, in turn, may increase the operatingefficiency of the hybrid vehicle. In particular, by considering thecondition of the fuel tank, and more specifically, estimating an amountof transferable fuel vapor residing in the fuel tank based on the amountof liquid fuel in the tank, fuel vapor purging operations may beperformed with increased precision. Further, by estimating thelikelihood of a fuel tank filling event occurring based on a durationsince a previous fuel tank filling event, a determination may be made toprioritize hybrid electric operation in favor of fuel vapor purgingoperation in order to improve operating efficiency of the hybridelectric vehicle. For example, if a fuel tank is substantially full ofliquid fuel and fuel vapor purging has occurred, the fuel vapor purgefrequency, rate, and/or duration may be reduced since the likelihood ofa fuel tank filling event is low. As another example, as the amount ofliquid in the fuel tank decreases the amount of fuel vapors residing inthe fuel tank increases as well as the likelihood of the fuel tank beingfilled, thus, the purge frequency, rate, and/or duration may beincreased in order to create space in the fuel vapor canister to handlean addition of fuel vapor entering the fuel vapor canister upon a fueltank filling event.

Furthermore, by considering the condition of the fuel tank, the fuelvapor purge rate may be adjusted to match engine operating conditions sothat the engine does not have to be adjusted strictly for fuel vaporpurging purposes which may reduce operating transparency to the vehicleoperator. In other words, fuel vapor purging may be performedopportunistically to meet vehicle operating conditions. In this way,fuel vapor emissions may be regulated without decreasing the operatingefficiency of the hybrid vehicle and providing improved operatingtransparency to the vehicle operator.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a hybrid propulsion system of thepresent disclosure;

FIG. 2 is a schematic diagram of an exemplary embodiment of an engine;

FIG. 3 is a schematic diagram of an exemplary embodiment of a fuelsystem;

FIG. 4 is a flow diagram that illustrates a routine for determining theamount of fuel vapor in the fuel vapor canister;

FIG. 5 is a flow diagram that illustrates a routine for monitoring afuel tank filling events;

FIG. 6 is a flow diagram that illustrates a routine for determining theamount of fuel vapor entering the fuel vapor canister upon a fuel tankfilling event;

FIG. 7 is a flow diagram that illustrates an exemplary strategy forpurging fuel vapor from a fuel vapor canister; and

FIG. 8 is a graphical representation of a default fuel vapor purgingapproach compared to an adaptive fuel vapor purging approach.

DETAILED DESCRIPTION

This disclosure outlines a strategy for fuel vapor purging that can beapplied to an engine system of a vehicle to improve engine operatingefficiency. In particular, the fuel vapor purge strategy may adjustpurging to deviate from an aggressive or prioritized purge that mayinterrupt efficient engine operation to an opportunistic purge approachwhich favors efficient engine operation based on known fuel system andengine operating parameters. The fuel vapor purge strategy may result inimproved robustness and increased operating efficiency of the enginewith improved operating transparency to the vehicle operator. In someembodiments, the fuel vapor strategy may be applied to a hybrid electricvehicle.

FIG. 1 schematically illustrates an example embodiment of a hybridpropulsion system for a vehicle. The hybrid propulsion system mayinclude at least an internal combustion engine 10 having one or morecylinders 30, a transmission 16, drive wheels 18 or other suitabledevice for delivering propulsive force to the ground surface, and one ormore motors 14. In this way, the vehicle may be propelled by at leastone of the engine or motor.

With regards to a full series type hybrid propulsion system, the enginemay be operated to generate a form of energy suitable for use by the oneor more motors. For example, with a full series type hybrid electricvehicle (HEV), the engine may generate electricity via a motor/generatorthat may be used to power an electric motor for propelling the vehicle.As another example, an engine may be operated to provide pump work to ahydraulic or pneumatic system that may be used to power a hydraulic orpneumatic motor for propelling the vehicle. As yet another example, anengine may be operated to provide kinetic energy to a flywheel orsimilar device for later application at the drive wheels.

With regards to a parallel type hybrid propulsion system, the engine andone or more motors may be operated independently of each other. As oneexample, an engine may be operated to provide torque to the drivewheels, while a motor (e.g. electric, hydraulic, etc.) may beselectively operated to add or remove torque delivered to the wheels. Asanother example, the engine may be operated with out the motor or themotor may be operated without the engine.

Further, with either series or parallel type propulsion systems, orcombinations thereof, an energy storage device may be included to enableenergy generated by the engine and/or motor to be stored for later useby the motor. For example, a regenerative braking operation may beperformed, where a motor/generator is used to convert kinetic energy atthe drive wheels to a form of energy suitable for storage at the energystorage device. For example, with regards to a HEV, the motor or aseparate generator may be used to convert torque at the wheels or torqueproduced by the engine into electrical energy that may be stored at theenergy storage device. A similar approach may be applied to other typesof hybrid propulsion systems including hydraulic, pneumatic, or thoseincluding flywheels.

In the illustrated example, one or more of motors 14 may be operated tosupply or absorb torque from the driveline with or without torque beingprovided by the engine. Still other configurations are possible.Therefore, it should be appreciated that other suitable hybridconfigurations or variations thereof may be used with regards to theapproaches and methods described herein.

Referring now to FIG. 2, one cylinder of a multi-cylinder engine isillustrated, as well as the intake and exhaust path connected to thatcylinder. Engine 10 as illustrated and described herein may be includedin a vehicle such as a road automobile, among other types of vehicles.In some examples, engine 10 may be included as a portion of a hybridpropulsion system including one or more other motors or engines, such asin the case of a hybrid electric vehicle (HEV). While the exampleapplications of engine 10 will be described with reference to a vehicle,it should be appreciated that engine 10 may be used in otherapplications not necessarily confined to vehicle propulsion systems.Engine 10 may be controlled at least partially by a control systemincluding controller 12 and by input from a vehicle operator 132 via aninput device 130. In this example, input device 130 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Combustion chamber (i.e.cylinder) 30 of engine 10 may include combustion chamber walls 32 withpiston 36 positioned therein. Piston 36 may be coupled to crankshaft 40so that reciprocating motion of the piston is translated into rotationalmotion of the crankshaft. Crankshaft 40 may be coupled to at least onedrive wheel of the passenger vehicle via a transmission system. Further,a starter motor may be coupled to crankshaft 40 via a flywheel to enablea starting operation of engine 10.

Combustion chamber 30 may receive intake air from intake passage 44 viaintake manifold 42 and may exhaust combustion gases via exhaust passage48. Intake passage 44 and exhaust passage 48 can selectively communicatewith combustion chamber 30 via respective intake valve 52 and exhaustvalve 54. In some embodiments, combustion chamber 30 may include two ormore intake valves and/or two or more exhaust valves.

Intake valve 52 may be controlled by controller 12 via electric valveactuator (EVA) 51. Similarly, exhaust valve 54 may be controlled bycontroller 12 via EVA 53. During some conditions, controller 12 may varythe signals provided to actuators 51 and 53 to control the opening andclosing of the respective intake and exhaust valves. The position ofintake valve 52 and exhaust valve 54 may be determined by valve positionsensors 55 and 57, respectively. In alternative embodiments, one or moreof the intake and exhaust valves may be actuated by one or more cams,and may utilize one or more of cam profile switching (CPS), variable camtiming (VCT), variable valve timing (VVT) and/or variable valve lift(VVL) systems to vary valve operation. For example, cylinder 30 mayalternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT.

Fuel injector 66 is arranged in intake passage 44 for injecting fueltherein in proportion to the pulse width of signal FPW received fromcontroller 12 via electronic driver 68. In this manner, fuel injector 66provides what is known as port injection of fuel which can be combustedinto combustion chamber 30. Fuel may be delivered to fuel injector 66 bya fuel system discussed in further detail below with reference to FIG.3. In some embodiments, combustion chamber 30 may alternatively oradditionally include a fuel injector arranged in cylinder 30 in aconfiguration that provides what is known as direct injection of fuelinto the combustion chamber.

Intake manifold 42 may include a throttle 62 having a throttle plate 64.In this particular example, the position of throttle plate 64 may bevaried by controller 12 via a signal provided to an electric motor oractuator included with throttle 62, a configuration that is commonlyreferred to as electronic throttle control (ETC). In this manner,throttle 62 may be operated to vary the intake air provided tocombustion chamber 30 among other engine cylinders. The position ofthrottle plate 64 may be provided to controller 12 by throttle positionsignal TP. Intake manifold 42 may include a mass air flow sensor 120 anda manifold air pressure sensor 122 for providing respective signals MAFand MAP to controller 12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. Emission control device 70 is shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 70 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof. In some embodiments, during operationof engine 10, emission control device 70 may be periodically reset byoperating at least one cylinder of the engine within a particularair/fuel ratio.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal, MAP, from sensor122. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold. Note that various combinations of the above sensors maybe used, such as a MAF sensor without a MAP sensor, or vice versa.During stoichiometric operation, the MAP sensor can give an indicationof engine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, may produce a predetermined number of equallyspaced pulses every revolution of the crankshaft.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine, and that each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Referring now to FIG. 3, an exemplary embodiment of a fuel system isillustrated. Fuel system 200 includes fuel storage tank 202. Fuel may bepumped from fuel storage tank 202 through fuel delivery pipe 206 to fuelrail 208 via fuel pump 204. Fuel rail 208 may disperse fuel to fuelinjectors 66 according to signal FPW from controller 12 to be injectedinto the ports of cylinder(s) 30. Fuel tank 202 includes filling tube210 for receiving fuel. Fuel filling tube 210 may be configured toextend away from fuel tank 202 to the external edge of the body of thevehicle so that it is accessible by a vehicle operator to fill the fueltank. Fuel filling tube 210 may be fitted with a fuel cap 212 which maybe removed during fuel tank filling. Fuel cap 212 may be configured tocreate a vapor-tight seal when connected to fuel filling tube 210 suchthat fuel vapor may be prevented from escaping from the fuel fillingtube and the fuel tank. Fuel cap sensor 214 may be positioned in asidewall of fuel filling tube 210. Fuel cap sensor 214 may send signalsto controller 12 indicating that fuel 210 cap has been removed or thatthe fuel cap is in an orientation that seals fuel tube 210. The fuel capsensor signals may be used as part of an exemplary fuel vapor purgestrategy discussed in further detail below with reference to FIGS. 4-7.

In some embodiments, the fuel system may not include a removable fuelcap but rather may include a one way seal disposed in the end of thefuel filling tube. In such a configuration, a sensor may be included inthe fuel system to detect when a fuel dispensing device enters the sealto dispense liquid fuel to the fuel tank. It should be appreciated thatother suitable seal devices may be used to seal fuel filling tube.

The liquid fuel level in fuel tank 202 may be determined by controller12 using sensor measurements. For example, in some embodiments, a liquidfuel level measuring device (not shown) that floats on the surface ofthe liquid fuel in the tank may determine the volume of liquid fuel inthe tank. Further, in some embodiments, sensor 216 may measure fuel tankpressure and a liquid fuel level may be derived from that pressuremeasurement. It should be appreciated that an indication of the liquidfuel level may be provided to the driver based on a determination viameasurement and/or calculation. Controller 12 may generate a fuel levelreading that may range between a full fuel tank and an empty fuel tankbased on the received measurements and/or the determination. Theindication may be displayed to the vehicle operator via a fuel levelindicator that may be used by the vehicle operator for fuel tank fillingpurposes.

Fuel system 200 further includes fuel vapor canister 220 that connectsto fuel tank 202 via vent pipe 218. In order to regulate pressure infuel tank 202, fuel vapor may flow from fuel tank 202 through vent pipe218 to fuel vapor canister 220. Fuel vapor canister 220 may trap fuelvapor flowing into the canister while allowing air filtered through thecanister to be vented to the atmosphere via an air vent (not shown). Insome embodiments, the fuel vapor canister may filter fuel vapor withcharcoal. The fuel vapor may adhere to the charcoal until the fuel vaporis purged.

Fuel vapor canister saturation may occur responsive to various operatingconditions and events. In one example, fuel tank filling may force fuelvapor residing in the fuel tank into the canister causing canistersaturation. As another example, heat and/or pressure generated duringvehicle operation may cause liquid fuel to evaporate creating fuel vaporwhich may be transferred into the canister causing saturation.

In order to avoid over saturation of the fuel vapor canister and releaseof fuel vapor to the atmosphere, fuel vapor may be purged from fuelvapor canister 220 through control of purge valve 222. Fuel vapor may bepurged from the fuel vapor canister using engine vacuum created duringengine operation. In one example, engine vacuum may be created byactuating throttle valve 64 and upon actuation of purge valve 222, fuelvapor may travel from fuel vapor canister 220 into the intake manifoldand enter cylinder(s) 30 for combustion. By introducing fuel vapor intothe cylinder and not into the atmosphere fuel economy may be improved.

It should be appreciated that other fuel vapor venting and purgingconfigurations may be implemented in the fuel system discussed above.For example, additional vent pipes and/or canisters may be used tofilter and contain fuel vapor. As another example, a fuel vapor purgingsystem may include multiple purge valves.

In some embodiments, a fuel vapor purging strategy may perform fuelvapor purging during low engine loads in order to decrease the impact onengine output. In particular, during fuel vapor purging the amount offuel vapor entering the cylinders may be unknown. The unknown amount offuel being combusted may lead to a reduction in accuracy of engineoutput control, particularly in an air/fuel ratio based engine controlstrategy. In other words, engine control may be reduced because it isunknown what is in the purge stream until after combustion. Accordingly,fuel vapor purging may be performed under low engine load conditions,such as for example idling conditions, in order to reduce variations inengine output.

During hybrid vehicle operation, in order to improve vehicle efficiencythe engine may be shutdown under some conditions. As a result of anengine shutdown condition, no engine vacuum is created in the intakemanifold and no combustion occurs. Thus, fuel vapor purging cannot beperformed. Accordingly, in a hybrid vehicle, since engine operation islimited, opportunity for fuel vapor purging is also limited.

In an exemplary embodiment, a fuel vapor purging strategy may be appliedto the above described engine and fuel system in vehicle that takesadvantage of known fuel system related parameters to adjust fuel vaporpurging in order to improve efficiency and drivability of the vehicle.Specifically, a determination to purge fuel vapor may be based on theliquid fuel level in the fuel tank and the duration between fuel fillingevents as part of an adaptive fuel vapor purge strategy. By applying theherein described fuel vapor purge strategy, fuel vapor purging may beconducted in a manner that may improve transparency to the vehicleoperator. Further, the strategy may be applied to a hybrid powertrain toreduce the release of fuel vapor emissions to the atmosphere and toimprove the operating efficiency of the hybrid powertrain.

The specific routines described below in the flowcharts may representone or more of any number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various acts or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments of the invention described herein,but is provided for ease of illustration and description. Although notexplicitly illustrated, one of ordinary skill in the art will recognizethat one or more of the illustrated acts or functions may be repeatedlyperformed depending on the particular strategy being used. Further,these figures may graphically represent code to be programmed into thecomputer readable storage medium in a controller.

In one example, the amount of fuel vapor currently residing in the fueltank may be estimated based on the amount of liquid fuel in the fueltank. The amount of fuel vapor residing in the fuel tank may be used,among other indicators, to define a prioritized purge approach thatallows for purging of the fuel vapor canister at a maximum purge rate inorder to prevent the release of fuel vapor into the atmosphere, evenwhen the fuel vapor canister is full. By determining the amount of fuelvapor in the fuel tank, the fuel vapor purging strategy may filter andpurge fuel vapor generated across the operating range of the vehicle.

FIG. 4 shows high-level routine 400 for determining the amount of fuelvapor residing in the fuel tank that may be transferable to the vaporcanister. Routine 400 may be used as part of a fuel vapor purge strategyto determine if fuel vapor purging may be conducted opportunistically inorder to not inhibit efficient vehicle operation. In particular, theestimated amount of fuel vapor transferable to the fuel vapor canistermay be used to determine a level of urgency or preference at which fuelvapor purging may be performed.

Routine 400 begins at 410, where the volume of the liquid fuel residingin the fuel tank is determined. In some embodiments, the liquid fuelvolume may be measured via a fuel level detection device. In someembodiments, the liquid fuel volume may be determined based oncalculation or estimation. For example, liquid fuel volume may bederived from measuring fuel tank pressure and estimated fuel consumptionsince the previous fuel tank fill. The liquid fuel volume may be used todetermine the amount of fuel vapor in the fuel tank which may correlateto the amount of fuel vapor transferred to the fuel vapor canisterduring a liquid fuel filling event. Thus, as liquid fuel is consumedmore fuel vapor may exist in the fuel tank which may transfer to thefuel vapor canister. In other words, the more liquid fuel that is in thetank, the smaller amount of fuel vapor that will be transferred to thecanister upon fuel tank filling.

Next at 420, the fuel tank pressure may be determined. In someembodiments, the fuel tank pressure may be measured via a pressuresensor. In some embodiments, the fuel tank pressure may be determinedbased on calculation or estimation. The fuel tank pressure may be usedto determine the amount of fuel vapor in the fuel tank.

Next at 430, the ambient temperature may be measured. The ambienttemperature may be used to estimate the amount of fuel vapor in the fueltank. In some embodiments, the amount of fuel vapor in the fuel tank maybe determined based on the measured ambient temperature and a forecastedambient temperature. For example, a forecasted ambient temperature maybe based on the time of day, day of year, and/or geographical location.In one example, a forecasted temperature during the middle of the daymay be high or increased over a forecasted temperature during the middleof the night. As another example, a forecasted temperature at a dayduring the winter may be lower than a forecasted temperature at a dayduring the summer.

Next at 440, the amount of fuel vapor in the fuel tank may be estimatedbased on a function (f(EV)) of the liquid fuel volume, the fuel tankpressure, and the ambient temperature. Note that in some embodiments,other fuel system operating parameters may be considered whendetermining the amount of fuel vapor in the fuel tank. The abovedescribed routine may be performed repeatedly throughout vehicleoperation in order to estimate the amount of fuel vapor in the fuel tankthat may be transferred to the fuel vapor canister during a fuel fillingevent.

In one example, the current fuel tank condition may provide anestimation of the amount of fuel vapor which may be transferred to thefuel vapor canister based on the likelihood of an impending fuel fillingevent. The fuel tank condition may be used, among other indicators, todeviate from the prioritized purge approach so that the fuel vapor purgerate may be adjusted and/or the duration of fuel vapor purgingoperations may be reduced. Optionally (or additionally), the frequencyof fuel vapor purging operations may be reduced based on the conditionof the fuel tank.

Furthermore, the future saturation state of the fuel vapor canister maybe determined to adjust the fuel vapor purging strategy from aprioritized purge approach in order to improve operating transparency tothe vehicle operator as well as to improve powertrain efficiency. In oneexample, the future saturation state of the fuel vapor canister may bean estimation of a likelihood of a fuel tank filling event occurring.The future saturation state of the fuel vapor canister may be used inconjunction with the determined amount of fuel vapor residing in thefuel tank to determine when to purge fuel vapor from the fuel vaporcanister. The future saturation state of the fuel vapor canister may belearned based on the liquid fuel filling habits of the vehicle operator.The fuel filling event learning routines will be discussed herein withreference to FIGS. 5 and 6.

Now turning to FIG. 5, an exemplary liquid fuel level monitoring routineis shown. Routine 500 monitors and records various fuel systemparameters related to fuel consumption and liquid fuel levels for aparticular fuel tank filling event. The routine may be performedrepeatedly in order to provide an indication of fuel consumption andfuel tank filling habits that may be used as part of an learning routinewhich may be used to determine (or estimate) the future saturation stateof the fuel vapor canister.

Routine 500 begins at 510, where fuel cap removal is detected by thecontroller. The fuel cap sensor may send a signal that indicates removalof the fuel cap for fuel filling purposes. Note that the controller maypoll repeatedly for this signal until it is detected. Alternatively, insome embodiments, a sensor disposed in the fuel filling tube may detectthe insertion of a fuel dispensing nozzle into the fuel filling tube andmay send a signal to the controller.

Next at 520, the duration since the previous fuel filling occurrence maybe calculated based on the elapsed time since the last fuel cap signalwas received. The elapsed time may be used to determine the durationbetween fuel tank filling occurrences. The duration between fuel fillingoccurrences may be used to determine the likelihood of the fuel tankbeing filled with liquid fuel.

Next at 530, the liquid fuel volume is measured and stored in memory.This measurement provides an indication of the liquid fuel volume priorto fuel tank filling. In some embodiments, the liquid fuel volume may becalculated from other fuel tank parameters.

Next at 540, fuel cap replacement may be detected based on receiving afuel cap signal. The indication may be used, among other signals, toidentify that fuel tank filling has occurred. Further, the signal mayalso be used to reset the timer used to calculate the duration betweenfuel tank filling events. Alternatively, in some embodiments, a sensordisposed in the fuel filling tube may detect the removal of a fueldispensing nozzle from the fuel filling tube and may send a signal tothe controller.

Next at 550, the liquid fuel volume is measured and stored in memory.The measured liquid fuel volume may be used to determine the amount offuel added to the fuel tank during fuel tank filling.

It should be appreciated that the above described routine may berepeated numerous times throughout vehicle operation in order to learnthe fueling habits of the vehicle operator. Further, the fuel systemparameters that are measured and stored in this routine may berepresentative of a single fuel filling event.

Routine 500 may be performed repeatedly to collect an aggregate amountof data representative of fuel consumption and fuel filling habits thatmay be considered when determining the current condition of the fueltank and the future saturation state of the fuel vapor canister as partof the fuel vapor purging strategy.

The fuel filling data aggregated through repeated operation of routine500 may be used to determine the future saturation state of the fuelvapor canister based on the likelihood of the a fuel tank filling eventoccurring. Specifically, the determined duration between fuel fillingevents may correlate to the likelihood of impending fuel tank fill. Inother words, as the duration increases so does the likelihood of a fueltank filling event occurring. Further, the amount of fuel being addedduring a liquid fuel filling event may be used to determine the amountof fuel vapor that may be transferred to the fuel vapor canister whenthe fuel tank was filled.

FIG. 6 shows high-level routine 600 for determining the futuresaturation state of a fuel vapor canister based on learned fuelconsumption and fuel filling habits derived from aggregate datagenerated from routine 500. Routine 600 begins at 610, where the averagefuel consumption between fuel tank filling events may be calculated. Thecalculation may be based on the aggregate fuel filling event datacollected by repeatedly performing routine 500 described above withreference to FIG. 5. In some cases, engine operation may be consideredin the fuel consumption calculation.

Next at 620, the average duration between fuel tank filling events maybe calculated. The calculation may be based on the aggregate fuelfilling event data collected by repeatedly performing routine 500described above with reference to FIG. 5. In some cases, the durationmay be based on elapsed time. In some cases, the duration may be basedon distance of vehicle travel. It should be appreciated that in someembodiments the duration may be based on other metrics.

Next at 630, the average fuel tank filling amount may be calculated. Thecalculation may be based on the aggregate fuel filling event datacollected by repeatedly performing routine 500 described above withreference to FIG. 5. The average amount of liquid fuel may be used toestimate an amount of fuel vapor likely to transfer to the fuel vaporcanister upon fuel tank filling.

Next at 640, the likelihood of a fuel tank filling event occurring maybe determined from the learned fuel tank filling data. The likelihood ofa fuel tank filling event occurring may be based on a function (f(FE))of, among other parameters, the duration between fuel filling events andthe level of liquid fuel in view of the average fuel consumption betweenfuel tank filling events. It should be appreciated that in someembodiments, other vehicle operating parameters may be considered inf(FE). For example, the time of day may be considered in f(FE). The timeof day may be weighted in the function since a fuel filling event may beless likely to occur during the night or early morning. Further, thetime of day at which a fuel tank filling event occurs may be a learnedparameter monitored in routine 500. Thus, the learned fuel tank fillinghabits of the vehicle operator may be considered in f(FE).

Routine 600 may be performed repeatedly throughout vehicle operation todetermine the likelihood of a fuel tank filling event occurring. Thelikelihood of a fuel tank filling event occurring (f(FE)) may beconsidered in conjunction with the transferable fuel vapor upon a fueltank filling event (f(EV)) to control hybrid vehicle operation as partof a fuel vapor purge strategy. The fuel vapor purge strategy will be infurther detail below with reference to FIG. 7.

As discussed above, fuel vapor purging may be limited by engineoperation. Thus, by adjusting the fuel vapor purge strategy to reducethe purge rate and/or duration and/or frequency of fuel vapor purgingaccording to the determination made in routines 400 and 600, operationof the IC engine in the hybrid vehicle for the purpose of fuel vaporpurging may be reduced which in turn may improve the operatingefficiency of the hybrid vehicle. Further, the amount of transferablefuel vapor, the likelihood of a fuel filling event occurring, and thedensity or content of the fuel vapor being purged may provide anestimation of the future saturation state of the fuel vapor canisterwhich may be used in the fuel vapor purge strategy to perform fuel vaporpurging opportunistically during hybrid vehicle operation.

For example, if it is determined that the likelihood of fuel tankfilling event occurring is low and/or the amount of transferable fuelvapor is low, then fuel vapor purging may be conducted only if the ICengine is currently operating. In other words, the fuel vapor purgestrategy may not operate the IC engine for the purpose of fuel vaporpurging. In this way, operating transparency may be improved since theIC engine may not be operated as frequently to purge fuel vapor and avehicle operator may perceive smoother and/or quieter hybrid vehicleoperation.

Furthermore, as discussed above, engine control may be affected duringfuel vapor purging since an unknown amount of fuel is being combusted.However, the content or density of fuel vapor being purged may beestimated based on an A/F ratio measured downstream from combustion.Thus, by determining the condition of the fuel tank and the futuresaturation state of the fuel vapor canister and adjusting the fuel vaporpurging strategy to reduce the purge rate and/or duration and/orfrequency of fuel vapor purging, engine control accuracy may bemaintained.

Now turning to FIG. 7, an exemplary embodiment of a fuel vapor purgingstrategy is shown. Fuel vapor purging routine (or strategy) 700 may takeinto consideration the current fuel vapor state of the fuel tank andfuture saturation state of the fuel vapor canister in order to purge thefuel vapor canister without unnecessarily reducing efficiency of thehybrid powertrain or vehicle operating transparency. Specifically, theroutine may determine if it is necessary to purge the fuel vaporcanister in order to prevent release of fuel vapor emissions into theatmosphere and may adjust engine operation to facilitate the purging.Further, the routine may use the condition of the fuel tank and thefuture saturation state of the fuel vapor canister to determine ifpurging may be desirable and/or possible without reducing the operatingefficiency of the hybrid powertrain and may adjust fuel vapor purgingoperations to purge opportunistically or to defer fuel vapor purgingoperation in favor of more efficient hybrid vehicle operation.

Routine 700 begins at 702, the amount of transferable fuel vapor in thefuel tank (f(EV)), the likelihood of a fuel tank filling event occurring(f(FE)), and a density or content of fuel vapor purged from the fuelvapor canister (f(VC)) may be applied in a function to determine a fueltank condition parameter that may be compared to a first threshold limit(Threshold Limit 1). The first threshold limit may define an upperregion where the fuel vapor canister is substantially filled to capacitywith fuel vapor. Under some conditions where the fuel vapor canister isat or beyond the first threshold limit, the addition of fuel vapor tothe fuel vapor canister may cause a release of fuel vapor to theatmosphere. As discussed above, f(EV) and f(FE) may be determinedaccording to the routines described in FIGS. 4-6. Further, f(VC) may bedetermined based on an amount (or density) of fuel vapor being purgedfrom the fuel vapor canister. In one example, f(VC) may be determinedbased on the A/F ratio measured after combustion to determine the amountof fuel vapor that is purged from the canister. By considering the purgedensity of the fuel vapor purged from the fuel vapor canister a futurestate of the fuel vapor canister may be estimated. For example, if fuelvapor purging is performed and the density of purged fuel vaporsdecreases then it may be projected that the amount of fuel vaporsresiding in the fuel vapor canister is being reduced and f(VC) may bereduced.

Accordingly, if it is determined that the fuel tank condition parameter(f(EV)*f(FE)*f(VC)) meets or exceeds the first threshold limit, routine700 moves to 720 where aggressive (or prioritized) fuel vapor purgingmay be performed. Otherwise if it is determined that fuel tank conditionparameter is less than the first threshold routine 700 moves to 750.

Note that the first threshold limit may be predetermined based onvarious fuel system parameters, such as for example, capacity of thefuel vapor canister, ambient temperature, vehicle operating mode, etc.In some embodiments, the first threshold limit may be calibratible suchthat the limit may be adjusted based on fuel system component lifespanand functionality parameters as well as other suitable fuel systemparameters.

In some embodiments, the fuel tank condition parameter(f(EV)*f(FE)*f(VC)) may be a function based on various fuel systemparameters as discussed above with reference to FIGS. 4-6. In someembodiments, f(FE) may be a weighted percentage that may influence f(EV)and/or f(VC). In some embodiments, the functions may be used to generatean estimate that may be compared to the threshold limit.

Continuing with routine 700, if it is determined that the fuel vaporcanister is substantially filled to capacity or likely to be filled withfuel vapor, aggressive (or prioritized) fuel vapor purging may beperformed in order to prevent a release of fuel vapor to the atmosphere.Fuel vapor may be considered to be purged aggressively because hybridvehicle operation may be interrupted in favor of the fuel vapor purgingin order to prevent an increase in fuel vapor emissions. In other words,fuel vapor purging may have priority over gains in operating efficiencyfrom hybrid electric or wide open throttle operation.

At 720, fuel vapor purging operation may be initiated and the IC enginemay be started so that fuel vapor purged from the fuel vapor canistermay be combusted.

Next at 730, the throttle valve position may be adjusted to provideengine vacuum to draw fuel vapor released from the fuel vapor canisterin the cylinders for combustion. Under some conditions, the throttlevalve may be positioned to generate a maximum vacuum to draw out fuelvapor from the fuel vapor canister so that the fuel vapor canister maybe purged quickly.

Next at 740, fuel vapor purging may be initiated via actuation of thefuel vapor purge valve. Fuel vapor purging may be performed for apredetermined duration. In some embodiments, the duration may beindicative of purging until an estimated amount of fuel vapor residingin the fuel vapor canister is below a desired amount. In someembodiments, the duration may be a predetermined amount of time. In someembodiments, the duration may be based on combustion cycles or anothersuitable engine operation parameter, such as the vapor content of thepurge flow (e.g., if the vapor content is low, then aggressive purge maybe transitioned into opportunistic or no purge).

At 750, the fuel tank condition parameter (f(EV)*f(FE)*f(VC)) may becompared to a second threshold limit (Threshold Limit 2). The secondthreshold limit may be less than the first threshold limit and maydefine a middle region where the fuel vapor canister contains some fuelvapor, but the fuel vapor canister may still have a capacity to receivemore fuel vapor from the fuel tank. In this region, fuel vapor may beselectively purged to increase the available capacity of the fuel vaporcanister. However, in this region, since the fuel vapor canister has thecapacity to receive more fuel vapor without releasing fuel vapor to theatmosphere, fuel vapor purging may be dictated by engine operation. Inother words, when the fuel tank condition parameter is determined to bein the middle region, fuel vapor purging may only be performed accordingto current vehicle operating conditions. For example, if the hybridvehicle is operating in an electric propulsion mode and the engine isnot operating, fuel vapor purging may be deferred in favor of gains inoperating efficiency through hybrid operation.

Thus, if it is determined that the fuel tank condition parameter meetsor exceeds the second threshold limit, then routine 700 moves to 760 andopportunistic fuel vapor purging may be performed. Otherwise, it may bedetermined that the fuel vapor canister is in a third region with a lowamount of fuel vapor residing in the fuel vapor canister and routine 700moves to 790.

At 760, it may be determined if the engine is operating. The engine maybe checked for operation so that hybrid operation is not interruptedstrictly for fuel vapor purging purposes. If it is determined that theengine is operating, then routine 700 moves to 770. Otherwise, if it isdetermined that the engine is not operating the routine ends.

Next at 770, it may be determined if the throttle valve is in a wideopen position. If it is determined that the throttle is wide open thenno engine vacuum is created and fuel vapor released from the fuel vaporcanister may not travel into the cylinder(s) for combustion. Moreover,the throttle valve would have to be positioned away from a wide openposition to create engine vacuum which may affect the operatingefficiency of the engine. Accordingly, if the throttle valve is wideopen fuel vapor purging operations are deferred in favor of efficientengine operation and the routine ends. Otherwise, if it is determinedthat the throttle is not wide open then it may be assessed that theconditions are suitable for fuel vapor purging and the routine continuesto 780 where fuel vapor purging may be performed.

At 780, purging of the fuel vapor canister is initiated. The operationmay begin by opening the fuel vapor purge valve. Fuel vapor may entercylinders of the engine at rate based on the condition of the throttlevalve. Fuel vapor purging may be conducted for a predetermined durationor until engine operation changes and conditions become unsuitable forfuel vapor purging. In one example, fuel vapor purging may be haltedupon the throttle valve being adjusted to a wide open position. Asanother example, fuel vapor purging may be halted when operation of theIC engine stops. If fuel vapor purging is not interrupted by a change invehicle operation, fuel vapor purging may be conducted until the fuelvapor canister is substantially empty or below a desired level, or theconditions for opportunistic purging are not met. In some cases, theduration of fuel vapor purging may be based on an estimate of the amountof fuel vapor residing in the fuel vapor canister which may be derivedfrom various fuel vapor purge parameters, such as for example, purgerate, canister capacity, ambient temperature, etc.

At 790, a condition of the fuel tank and/or vehicle operation may not besuitable for opportunistic fuel vapor purging. In some embodiments,opportunistic fuel vapor purging may not be conducted because it isdetermined that the current state of the fuel vapor canister issubstantially empty or the amount of fuel vapor is below a predeterminedlevel.

In the above described fuel vapor purging strategy, a prioritized purgeapproach may be performed in order to prevent the release of fuel vaporemissions to the atmosphere. In particular, the prioritized purgeapproach may interrupt hybrid operation in favor of preventing anincrease in vehicle emissions due to the release of fuel vapor to theatmosphere. In other words, the prioritized purge approach may beperformed in favor of electric operation or other efficient operation ofthe hybrid vehicle in order to prevent an increase in emissions.

Furthermore, the fuel vapor purging strategy may deviate from theprioritized purge approach when the fuel vapor canister is determinednot to be full and may instead follow an opportunistic purge approach.The opportunistic purge approach may permit fuel vapor purging to occurwithout lowering hybrid powertrain efficiency. In particular,opportunistic fuel vapor purging may be deferred in favor of hybridoperation or other more efficient engine operation when possible.Moreover, opportunistic fuel vapor purging may be conducted according tocurrent operating conditions. By purging according to the condition ofthe fuel tank, more specifically, the amount of fuel vapor residing inthe fuel tank and the likelihood of a fuel tank filling event occurring,fuel vapor purging (i.e. rate/duration/frequency) may be adjusted toimprove operating efficiency of the hybrid vehicle and operatingtransparency to the vehicle operator. In this way, the frequency ofengine operation solely for the purpose of fuel vapor purging may bereduced and efficiency of the hybrid powertrain may be maintained.

Note that in some embodiments, the above described fuel vapor purgingstrategy may be incorporated into an engine control strategy and/or ahybrid powertrain control strategy.

FIG. 8 graphically illustrates fuel vapor purging operation according tothe various fuel vapor purging approaches in the fuel vapor purgingstrategy described above with reference to FIG. 7. In particular, thefuel tank condition parameter (f(EV)*f(FE)*f(VC)) is graphicallyrepresented throughout vehicle operation. The fuel tank conditionparameter may be categorized according to three different fuel vaporpurging regions based on the first threshold (Threshold 1) and thesecond threshold (Threshold 2). Namely, when the fuel tank conditionparameter is above the first threshold in a first region that isindicative of the fuel vapor canister being substantially full,aggressive fuel vapor purging may be performed. The fuel tank conditionparameter may be in a second region indicative of the fuel vaporcanister being partially filled when the fuel tank condition parameteris between the second threshold and the first threshold, andopportunistic fuel vapor purging may be performed. The fuel tankcondition parameter may be in a third region indicative of the fuelvapor canister having a low amount of fuel vapor or being substantiallyempty when the fuel tank condition parameter is below the secondthreshold, an no fuel vapor purging may be performed.

Thus, by adjusting fuel vapor purging operation based on the fuel tankcondition parameter fuel vapor purging may be performed to reduce orsubstantially eliminate the amount of fuel vapors released to theatmosphere. Moreover, fuel vapor purging operations may be reduced ormodified to improve operating efficiency of the vehicle as well as toimprove operating transparency perceived by the vehicle operator.

It should be appreciated that in some embodiments the fuel vapor purgingstrategy may include all of the above described routines. Alternatively,in some embodiments the fuel vapor purging strategy may include onlyselected routines to adjust the fuel vapor purging strategy.

Furthermore, it should be appreciated that the above described fuelvapor purging strategy may be applied to a non-hybrid electric vehicle(e.g. a vehicle propelled only by an internal combustion engine). Inthis strategy, wide open throttle operation may be interrupted in favorof fuel vapor purging operation when a fuel tank condition parametermeets or exceeds a threshold limit. Further, if the fuel tank conditionparameter does not meet or exceed the threshold limit fuel vapors may beselectively purged when the vehicle not operating in a wide openthrottle mode.

As described above, the fuel tank condition parameter may be based on,among other parameters, an amount of liquid fuel residing in the fueltank which may be used to estimate an amount fuel vapor transferable tothe fuel vapor canister upon a fuel tank filling event and the durationsince a previous fuel tank filling event which may be used to estimatethe likelihood of a fuel tank filling event occurring. In someembodiments, the fuel tank condition parameter may be based on the fuelvapor content that is being purged from the fuel vapor canister.

Accordingly, vehicle operation may be adjusted away from wide openthrottle operation to purge fuel vapor in order to prevent a release offuel vapor to the atmosphere. Moreover, fuel vapor purging may beperformed opportunistically according to current vehicle operationwithout intrusive interruption for the purpose of fuel vapor purging. Inthis way, operating efficiency and robustness may be improved since thefrequency, rate, and/or duration of fuel vapor purging may be reduced.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,1-4, 1-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A method of controlling fuel vapor purging in a hybrid electricvehicle capable of selectively operating an internal combustion engine,the method comprising: determining a fuel tank condition parameter basedon an amount of liquid fuel residing in a fuel tank of the hybridelectric vehicle and a duration since a previous fuel tank fillingevent; in response to the fuel tank condition parameter exceeding athreshold limit, initiating operation of the internal combustion engineand purging fuel vapor from the fuel vapor canister for a predeterminedduration; and in response to the fuel tank condition parameter beingless than the threshold limit, selectively purging fuel vapor from thefuel vapor canister based on an engine operating condition.
 2. Themethod of claim 1 wherein the engine operating condition includescombustion in at least one cylinder of the internal combustion engine.3. The method of claim 1 wherein the engine operating condition includesa position of a throttle valve of the internal combustion engine.
 4. Themethod of claim 3 wherein fuel vapor purging is not performed when thethrottle valve is in a wide open position.
 5. The method of claim 1wherein the duration since the previous fuel tank filling event isdetermined based on detection of at least one of a fuel cap sensorsignal and a fuel nozzle insertion signal.
 6. The method of claim 1further comprising: comparing the fuel tank condition parameter to asecond threshold limit lower than the first threshold limit; in responseto the fuel tank condition parameter being less than the secondthreshold limit, suspending fuel vapor purging operation.
 7. The methodof claim 1 wherein selective fuel vapor purging is performed for atleast one of a predetermined duration and until a change in operatingmode of the hybrid electric vehicle.
 8. The method of claim 7 whereinthe predetermined duration is based on vapor content of the purge of thefuel vapor from the fuel vapor canister.
 9. The method of claim 1wherein the fuel tank condition parameter is based on a learned fuelparameter.
 10. The method of claim 9 wherein the learned fuel parameterincludes at least one of average fuel consumption and average amount ofliquid fuel added during a fuel tank filling event.
 11. The method ofclaim 1 wherein the fuel tank condition parameter is based on fuel tankpressure.
 12. A method of controlling fuel vapor purging in a vehicle,the method comprising: selectively operating an internal combustionengine; during operation of the internal combustion engine, performing afuel vapor purge operation based on an amount of liquid fuel in a fueltank of the hybrid electric vehicle and a duration between liquid fuelfilling events.
 13. The method of claim 12 further comprising: comparingthe amount of liquid fuel in the fuel tank and the duration betweenliquid fuel filling events to a threshold limit; in response to theamount of liquid fuel in the fuel tank and the duration between liquidfuel filling events exceeding the threshold limit, initiating operationof the internal combustion engine; and purging fuel vapor from the fuelvapor canister for a predetermined duration.
 14. The method of claim 13further comprising: in response to the amount of liquid fuel in the fueltank and the duration between liquid fuel filling events being less thanthe threshold limit, selectively purging fuel vapor from the fuel vaporcanister based on an operating condition.
 15. The method of claim 14wherein the operating condition includes combustion in at least onecylinder of the internal combustion engine and a throttle valve of theinternal combustion engine positioned not at wide open.
 16. The methodof claim 15 wherein selective fuel vapor purging is halted responsive toa change in operating mode of the hybrid electric vehicle.
 17. Themethod of claim 15 wherein the predetermined duration includes apredetermined amount of time.
 18. A fuel system for a vehicle,comprising: a fuel tank for storing liquid fuel supplied to an internalcombustion engine for combustion; a fuel vapor canister in fluidcommunication with the fuel tank; a purge valve for releasing fuel vaporfrom the fuel vapor canister into an intake manifold of the internalcombustion engine; a throttle valve positioned in the intake manifold;and a controller, the controller in response to a fuel tank conditionparameter exceeding a threshold limit, adjusting a position of thethrottle valve away from a wide open position and actuating the purgevalve for a predetermined duration, and in response to a fuel tankcondition parameter being less than a threshold limit, during operationof the internal combustion engine, selectively actuating the purge valvebased on an operating parameter of the engine.
 19. The system of claim18 wherein the fuel tank condition parameter is based on at least one ofan amount of liquid fuel stored in the fuel tank and a duration since aprevious fuel tank filling event.
 20. The system of claim 18 wherein theoperating parameter of the engine includes the throttle valve positionedaway from wide open.